Support coils are used to radially support a resiliently expanded tube material, such as an insulating tube or sleeve body, during the insertion of an electrical component therein. For example, the insulating tube and/or sleeve body may be used to electrically insulate and/or seal electrical components, such as cable couplings or cable plug connectors, in power engineering applications. Because high electrical voltages above 100 kV can be applied to the electrical components, the insulating tube is formed to have a thick wall and is made of a material with good electrical insulation properties, such as silicone. The tube material may be, for example, a cold shrink tube, and is formed to resiliently adapt to an outer contour of the electrical component such that the electrical component is insulated and sealed as tightly as possible. The tube material may have a diameter that is capable of expanding up to four times its original size prior to fitting of the electrical component therein. The electrical component can therefore be easily introduced into the tube material.
In order to keep the tube material expanded prior to fitting of the electrical component, a support coil is inserted into the tube material. The support coil resiliently expands the tube material and absorbs the restoring force of the tube material due to the resilient expansion thereof. The support coil absorbs, for example, compressive forces of about 10 bar. The electrical component is then inserted into the support coil. The support coil is then removed from the tube material to allow the tube material to tighten around the electrical component. Because the support coil is an extruded profile body consisting of a plurality of windings, the support coil may be removed from the tube material by manually unwinding or unraveling the support coil in a longitudinal axis. As the support coil gradually unravels, the tube material automatically tightens around the electrical component to be insulated. The unwound extruded profile body may then be extracted from the tube material.
In view of the foregoing, the support coil must be formed such that the support coil can permanently withstand the high pressure emanating from the expanded tube material and can be removed manually from the tube material. It is also important for the support coil to have a wall thickness that is as low as possible to allow sufficient overall space for the introduction of the electrical component therein. In order to meet these requirements, it is known to join together end faces of the windings of the extruded profile body of the support coil in a material-uniting manner, for example, by welding or bonding. It is additionally known to form the end faces of the windings of the extruded profile body of the support coil such that adjacent end faces of the windings interlock. Examples of these types of support coils are described in U.S. Pat. No. 5,087,492, EP 0 619 636 A1, WO 93/22816, WO 83/00779, DE 198 20 634 C1, EP 0 399 263 A2, U.S. Pat. No. 5,670,223 and WO 96/24977.
A problem exists in the above-described support coils in that the material-uniting connection between the end faces of the windings is not uniformly tight. A non-uniform connection between the end faces of the windings can cause the detaching forces required for manually unwinding the extruded profile body to markedly fluctuate, such that manually separating the connected end faces can, on unraveling of the windings, become difficult or even impossible. Additionally, a non-uniform connection between the end faces of the windings can cause the support coil to break or fail under the load of the resiliently expanded tube material.